1. Field of the Invention
The present invention relates to the field of viral vaccines. In particular, the present invention relates to modification of immunogenic epitopes of the hepatitis C virus (HCV) core protein to elicit an enhanced immune response against HCV.
2. Background Art
Hepatitis C virus (HCV) is a single stranded RNA virus responsible for the majority of non-A non-B hepatitis (1). Infection by HCV frequently evolves to chronicity and in many cases leads to liver cirrhosis and hepatocellular carcinoma (2). The cellular immune response is thought to be responsible for viral clearance in many viral infections (3-7) and in the case of HCV, a cytotoxic T lymphocyte (CTL) response is present in acutely and chronically infected patients (8-14), but its role in viral clearance has not been elucidated. CTL responses have been detected in peripheral blood mononuclear cells (PBMC) and in intrahepatic lymphocytic infiltrate in patients with chronic hepatitis (15) and in the liver of infected chimpanzees (16), indicating that in these cases the virus is able to persist despite this immune response (17). The reasons for the inadequacy of this immune response in chronically infected patients are not known (18).
CD8+ CTL recognize antigens as peptides presented by class I molecules of the major histocompatibility complex (MHC) on the cell surface. These peptides are usually 8-10 amino acids long and are generated after processing of intracellular antigens (3,19-21). Analysis of peptides presented by MHC class I molecules has led to the definition of several sequence patterns or motifs (22-24) for peptides that bind to each particular MHC allele or group of alleles (supermotif) (25). These motifs are based on the presence in precise positions in the peptide sequence of several amino acids (agretopic residues) called anchor residues (22,26), responsible for interactions between peptide and MHC molecule, as well as other secondary positions that may help in stabilizing these interactions (27-29). The use of these motifs to identify peptides able to bind to MHC molecules, together with the development of MHC-peptide binding assays, has led to the characterization of many CTL epitopes in the HCV polypeptide presented by different MHC molecules (9,10,12,30). Among the best studied motifs is that of HLA-A2.1, which is prevalent in a high percentage of the population (31). Several reports describe the binding motif for this allele, pointing out the importance of anchor as well as secondary residues. Also, MHC binding has been correlated with immunogenicity in different mouse and human systems (30,32-37).
Despite the presence of the typical anchor residues, the binding capability of a peptide epitope may vary, depending on the other secondary residues. Thus, the presence of certain amino acids in secondary positions may enhance or impair a peptide's binding ability (28,38,39). Other amino acids (epitopic residues) are responsible for recognition by the T cell receptor (TCR). Thus, T cell response is triggered by interactions in the trimolecular complex: MHC-antigenic peptide-TCR, together with other co-stimulatory molecules (40,41). These interactions occur between the antigenic peptide and pockets in the structure of both MHC and TCR molecules and changes in the amino acid sequence of the peptide may affect any of these interfaces.
Because of the inadequacy of the immune response in HCV-infected individuals, there exists a great need to enhance the immune response to HCV immunogenic epitopes without impairing MHC binding affinity or T cell recognition. The present invention overcomes the previous limitations and shortcomings in the art by providing immunogenic peptides of HCV core protein which elicit an enhanced immune response, methods for making these peptides and methods for using these peptides for a variety of therapeutic, diagnostic and prognostic applications.